Paul,
What are these mirrors to which you refer. I don't think my mate can be aware of them and it would be nice to point him in the right direction.
It is a legal requirement to have two mirrors on a vehicle registered from 1st June 1978, one must be an offside mirror. Penalty £50 and immediate prohibition.
Keith,
Being aware of your position in life, that is why I asked the question because when you remove the door/ side screens on a C7, you loose both of the mirrors.
Caterham sell these 'arms' and describe them as 'SVA mirror mount kit' and charge the princely sum of £30.20 per mirror. It doesn't include the mirror head as this is taken off the mirror mounted to the sidescreen. There is a picture on their parts website.
Frankly though, it should be cheaper and just as easy to find an offside mirror through one of the various suppliers like SVA or Holden etc.